The present invention relates to a light emitting device such as a light emitting diode (LED) or a laser diode (LD) which includes a three-dimensional photonic crystal and emits light by injecting a carrier into an active medium.
A conventional general semiconductor light emitting device has electrodes, clad parts, and an active part. A hole is injected into the active part from a P-type electrode through a P clad part and an electron is injected into the active part from an N-type electrode through an N clad part. Both carriers are recombined in the active part and spontaneous emitted light that has energy corresponding to an energy gap of the active part is emitted. In particular, when a resonator is formed so as to include the active part with a cleaved surface or the like, stimulated emitted light is generated by a light amplification by the resonator to generate a laser beam.
However, all of the injected carriers do not necessarily contribute to a desired luminescence. In other words, some of the carriers are consumed by nonradiative recombination such as surface recombination or by radiative recombination which generates light having a wavelength other than a desired one. These recombinations cause a loss that reduces an internal efficiency.
As a method of reducing the loss caused by the radiative recombination which generates the light having the wavelength other than the desired one, a method of controlling the spontaneous emission by a photonic crystal to obtain high internal efficiency is proposed in “Physical Review Letters, Vol. 58, pp. 2059, 1987”. The method proposed in the “Physical Review Letters, Vol. 58, pp. 2059, 1987” is to limit a wavelength band of light capable of existing in the vicinity of the active layer by using “photonic band gap” which the photonic crystal has, to suppress the spontaneous emitted light which has the wavelength other than the desired one. This way, it is desirable to use a three-dimensional photonic crystal forming a three-dimensional permittivity distribution in order to control the spontaneous emission to obtain the high internal efficiency.
Japanese Patent Laid-Open No. 2001-257425 discloses a laser element using a three-dimensional photonic crystal. In the structure disclosed in Japanese Patent Laid-Open No. 2001-257425, an active part is formed in the three-dimensional photonic crystal, and carriers are injected into the photonic crystal through a contact layer from a metal electrode provided outside the photonic crystal. The injected carriers are conducted in the photonic crystal structure to be connected to a carrier conducting route formed as a line defect to be guided to the active part. The carrier conducting route concurrently holds the light waveguide. The light generated by the carrier recombination in the active part is taken out of the photonic crystal through the light waveguide.
In the structure disclosed in Japanese Patent Laid-Open No. 2001-257425, the volume of the resonator is smaller than that of a conventional laser diode. Therefore, heat is generated by the concentration of the carriers in a narrow area in the vicinity of the active part. As a result, the carrier overflow occurs because of the temperature rise in the active part, and the decrease in internal efficiency is caused. Since the optical characteristic of the resonator changes if the temperature change occurs in the active part, it is undesirable to cause the temperature change from this respect.
In the structure disclosed in Japanese Patent Laid-Open No. 2001-257425, since a waveguide which is used for taking out light outside the light emitting device is provided in both a P clad part and an N clad part, a mirror with a high reflectance needs to be formed on an edge surface of the waveguide at one side to obtain a high taking-out efficiency. However, the reflected light from the waveguide where the mirror is arranged returns to the resonator to cause a noise.